The subject matter of the present invention relates generally to a supported plasma sputtering apparatus which is capable of high deposition rates over a wide area, and in particular to triode sputtering apparatus having plasma shaping electrodes to provide a high density plasma without the use of any externally applied magnetic field to enable a more uniform deposition of sputtered material over a wide area. A "supported plasma" sputtering apparatus is one in which the plasma is maintained or supported by an electron discharge from a thermionic cathode to an anode and the sputtering target is immersed in such plasma. The plasma shaping electrodes shape the electrical field in the electron discharge region between the cathode and anode and in the sputter region between the target and substrate member to provide a high density plasma which increases the sputter deposition rate and enables a large area deposit of substantially uniform thickness. A radio frequency potential may be applied to the target to increase the sputtering rate and apparently increase the plasma density, which results in improved deposit thickness uniformity and greater deposit density, partially due to lower pressure. A long stable sputtering operation is achieved by maintaining the electron discharge using different types of anodes surrounding the target, which either shield anode surface portions from exposure to sputtering material or remove sputtered coatings on the anode by heating, or to simultaneously mix sputtered metal from the auxiliary target with sputtered insulator from the main target so that the resultant coating is conductive.
The sputtering apparatus of the present invention is especially useful in sputtering metal, insulator or semiconductor materials over large areas, such as during the formation of solar panel photocells for the conversion of light to electrical power.
Previously it has been proposed in the article, "High Rate RF Sputtering System", Journal of Vacuum Science and Technology, Volume 7, No. 2, by D. H. Grantham et al, pages 343-346, published 1969, and in U.S. Pat. No. 3,901,784 of D. J. Quinn et al, granted Aug. 26, 1975, to deposit insulating material at a high deposition rate using radio frequency power. However, a magnetic field was provided in the sputter region to increase the deposition rate and no plasma shaping electrodes were employed so that a relatively small target area was sputtered and the sputtered deposit on the substrate would have a nonuniform thickness. Similar results would be achieved by triode sputtering apparatus shown in U.S. Pat. No. 3,514,391 of Hablanian et al and U.S. Pat. No. 3,616,452 of Bessot et al, both of which apply radio frequency fields to insulating targets but employ magnetic fields in the sputter region which would result in a small area deposition and would produce nonuniform thickness deposits. An R.F. sputtering apparatus using a finned or ribbed anode to prevent sputtered material from completely coating such anode is shown in U.S. Pat. No. 3,514,391 and in the article, "Initial Work on the Application of Protective Coatings to Marine Gas Turbine Components by High Rate Sputtering", by E. D. McClanahan et al in publication 74-GT-100 of the American Society of Mechanical Engineers, published March, 1974. None of these prior references disclose the use of plasma shaping electrodes separate from the anode which are connected to a more negative potential and shape the electrical fields in the electron discharge region and sputter region to increase the plasma density without using a magnetic field in the manner of the present invention.